Differential pressure sensors which detect the amount of displacement of a diaphragm which is disposed between two chambers, and output a pressure difference signal, are, for example, disclosed in Patent Citations #1 and #2. The differential pressure sensor which is disclosed in Patent Citation #1 has a cantilevered plate spring one end of which is fixed to a housing and the other end of which contacts the diaphragm, and the position of the point of contact between the cantilevered plate spring and the diaphragm changes according to the pressure difference between the chambers, with an electrical signal having a level which corresponds to the position of this point of contact being outputted as a pressure difference signal. The cantilevered plate spring described above is formed in a shape which, as a whole, extends in a single direction from its fixed end to its contact point with the diaphragm.
And, in the differential pressure sensor which is disclosed in Patent Citation #2, a piston is contacted against a diaphragm, this piston is elastically pushed in the direction of the diaphragm by a coil spring, and an electrical signal having a level which corresponds to the position of this piston is outputted as a pressure difference signal. In order always to keep the coil spring in a dead straight form, the coil spring is inserted into a narrow tube.    Patent Citation #1: Japanese Laid-Open Patent Publication Showa 61-230037 (for example FIGS. 2 and 8);    Patent Citation #2: Japanese Laid-Open Utility Model Publication Heisei 4-113044.